1. Field of the Invention
The invention relates to a vapor-permeable laminate with at least one first outer layer and at least one second outer layer, the outer layers having perforations and being joined to one another in such a way that the perforations of the first outer layer do not coincide with the perforations of the second outer layer, and a structure having pores being provided between the outer layers.
2. Description of Related Art
Vapor-permeable laminates of the aforementioned type are microporous webs or sheets which are structured by their fine-pored configuration in such a way that vapor molecules can pass or diffuse through them in a controlled manner. Laminates of this kind, which are also referred to as diffusion-open membranes, are intended to ensure a breathable wall or roof structure in the construction industry. It is intended that excess moisture in the air of a room can be diffused out through the laminate in a controlled manner, in order to prevent problems, such as moisture damage in the region of the insulating layers located in the wall or roof structure. At the same time, it is intended that sufficient seal-tightness is ensured. It is a disadvantage of the laminates of the aforementioned kind that are known from practice that the mechanical properties and durability of these products are limited.
The application of vapor-permeable laminates of the aforementioned kind is not, however, restricted to the aforementioned use. Use is also possible in other areas in which, on the one hand, seal-tightness under exposure to liquids, and on the other hand vapor, permeability are required.
International Patent Application Publication WO 2006/072604 A2 already discloses a laminate of the aforementioned kind. In the case of this laminate, two microstructured and perforated sheets are joined to one another in such a way that the structured sides of the individual sheets lie opposite one another and the structures thereby run crosswise. The perforation holes in the individual planes of the sheets must not coincide with one another during lamination, since otherwise it is possible for liquid to pass directly through the laminate and the composite is consequently not seal-tight. In principle, it is intended here that the distance between the perforations in the two planes is of such a size that the diffusion path for gas to pass through is not too great, but there are enough barrier locations between the two perforations to effectively prevent moisture from passing through. In the case of this known laminate, it is provided for this purpose that the distance between the first and second outer layers, and consequently the channel height, should be less than 200 μm. To achieve seal-tightness under a static water column of 100 cm, the distance between the two outer layers, and consequently the channel height, must be 50 μm. If a lower level of seal-tightness is required, a greater distance between the outer layers can accordingly be realized. The individual figures of WO 2006/072604 A2 reveal that, in the best case, the channels have a width which is twice the channel height. Generally, the channel width is many times greater than the channel height.
Since the web described in WO 2006/072604 A2 does not exist in practice, the applicant has invested considerable effort in preparing test specimens of webs of this kind. Preparation of such specimens involves considerable effort particularly because webs with microstructures of this kind previously did not exist. It was also problematic for webs of this kind to be laminated in such a way that the channel structure is not adversely affected during the lamination, with the consequence that the microporosity and, as a result, the vapor permeability suffer. After preparing specimens, tests were carried out by the applicant to check the seal-tightness and vapor permeability. It was found during these tests that the laminates produced according to WO 2006/072604 A2 are sufficiently vapor-permeable, but exhibit passage of water through them, and consequently lack of seal-tightness, even under low static water columns of less than 20 cm.